More snow accumulating in the mountains is pretty much widely understood here in Montana. Snowfall totals can vary greatly over short distances because elevation can change rapidly here in the state. But why exactly is that?
One of the basic principles of meteorology is that temperature decreases as altitude or elevation increases. Change in temperature with height is called the lapse rate. In a storm like the one we had over the weekend, with humidity around 100%, the average lapse rate in the lower atmosphere is 3.5 degrees Fahrenheit cooler for every thousand feet gained in elevation. When air is dry, the lapse rate is even greater at 5.5 degrees per 1000 feet.
With a storm like this past weekend with temperatures in the 30s and low 40s, a difference of a few hundred feet in elevation can mean the difference between rain or snow.
Parts of the Helena Valley had no accumulation while the higher elevations around town near 5000 feet had a foot or more. Even in Great Falls, a few inches fell in town and near Malmstrom Air Force Base, but just a couple hundred feet up the hill toward the airport, there were several inches more.
Orographic lift also contributes to more precipitation in the mountains. As moisture-laden air is pushed upwards by geography, the atmosphere releases that moisture. As air descends downward in elevation, the atmosphere can hold more moisture limiting the precipitation.
So if you love snow, move to higher ground. If not, head to the lower elevations, or Florida.